Computer Communication Networks (Sub. , Code : 10 EC 71) 01 820 Unit-I introduction 1
Unit - 1 Overview Layered tasks OSI Model Layers in OSI model TCP/IP Suite Addressing Telephone and cable networks for data transmission, Telephone networks Dial up modem DSL Cable TV for data transmission. 01 820 Unit-I introduction 2
Network Models 01 820 Unit-I introduction 3
Layered Tasks We use the concept of layers in our daily life. As an example, let us consider two friends who communicate through postal mail. The process of sending a letter to a friend would be complex if there were no services available from the post office. Sender, Receiver and, Carrier Higher Layer Middle Layer Lower layer Hierarchy Tasks must be done in the given order 01 820 Unit-I introduction 4
THE OSI MODEL Established in 1947, the International Standards Organization (ISO) is a multinational body dedicated to worldwide agreement on international standards. An ISO standard that covers all aspects of network communications is the Open Systems Interconnection (OSI) model. It was first introduced in the late 1970 s. ISO is the organization. OSI is the model. 01 820 Unit-I introduction 5
Layers in the OSI Model “Please Do Not Touch Steve’s Pet Alligators” 01 820 Unit-I introduction 6
Reasons For Layering Layered networking model is advantageous because • Divides networking into less complex components • Enables programmers to specialize in a particular level • Allows upgrades to a specific layer without effecting other layers • Encourages interoperability • Allows for standardized interfaces 01 820 Unit-I introduction 7
The interaction between layers in the OSI model 01 820 Unit-I introduction 8
Reasons For Layering Layered Architecture Peer to peer Process • The process on each machine that communicates at a given layer are called peer-to-peer process. Interfaces Between Layers • Interface defines the information and services a layer must provide for the layer above it. Organization of the layers (subgroups ) • Layers 1, 2, and 3 are the network support layers • 5, 6, and 7 as a user support layers • Layer 4, Transport layer links the two subgroups 01 820 Unit-I introduction 9
The interaction between layers in the OSI model • The OSI model is composed of seven ordered layers. • Within a single machine each layer calls upon the services of the layer just below it. • Layer 3 uses the services of layer 2 and provide services to layer 4 • Between machines, layer x on the machine communicates with layer x on another machine. • Communication is governed by an agreed upon series of rules and conventions called protocols. (A protocol is a rule which guides how an activity should be performed, especially in the field of diplomacy. In computing, a protocol is a convention or standard that controls or enables the connection, communication, and data transfer between two computing endpoints. ) • The process on each machine that communicates at a given layer are called peer-to-peer process. 01 820 Unit-I introduction 10
Physical layer • The physical layer is concerned with transmitting raw bits over a communication channel. • It deals with the mechanical, electrical, and timing interfaces, and the physical transmission medium, which lies below the physical layer. • Physical Characteristics of interfaces and media, Representation of bits, Date rate, Synchronization of bits, Physical topology, Transmission mode(eg. , Simplex). 01 820 Unit-I introduction 11
Physical layer has the following responsibilities Physical characteristics of interfaces and medium • Cable • Connectors • Interfaces • Transmission Medium • Cable/wire • Radio waves • Infrared • Fiber/glass Representation of bits • Bits must be encoded into signals- electrical, optical. Type of encoding (binary encoding as voltages (Manchester encoding method) • Transmission of the signal on the medium Synchronization of bits • Tx and Rx clocks must be synchonized. 01 820 Unit-I introduction 12
Physical layer has the following responsibilities Data Rate • Duration of the bit Physical Topology • How device are connected • Ring, Bus, Mesh, star Topology Transmission mode • Simplex, half duplex, duplex. 01 820 Unit-I introduction 13
Physical layer 01 820 Unit-I introduction 14
Data link layer • Responsible for moving frames from one hop (node) to the next • Framing: Divides the stream of bits received from network layer into manageable data units called frames. • Physical addressing: Adds a header to the frame to define the sender and/or receiver of the frame. • Flow Control: If the receiver is slower than the transmitter • Error Control: Retransmit for damaged frames, recognition duplication • Access Control: 01 820 Unit-I introduction 15
Hop-to-hop delivery 01 820 Unit-I introduction 16
Data link layer Data Link sublayers • Logical Link Control (LLC) layer • Defines how data is packaged (frames) • Provides the linking function between the Physical Layer and the higher layers • Media Access Control (MAC) layer • Media access method • Provides a unique identifier for the NIC (Physical address) 01 820 Unit-I introduction 17
Data link layer • Type ipconfig/all at command prompt 01 820 Unit-I introduction 18
Network layer • Responsible for source to destination delivery of individual packet. • Logical addressing: Physical address used only for locally • Routing: 01 820 Unit-I introduction 19
Source-to-destination delivery 01 820 Unit-I introduction 20
Transport layer • Responsible for process-to-process delivery of the entire message. • A process is an application program running on a host. • Transport layer ensures the whole message arrives intact and in order, overseeing both error control and flow control at the source-to-destination level 01 820 Unit-I introduction 21
Transport layer has the following responsibilities End-to-end error free transmission and delivery Segmentation and reassembly: Divided into transmittable segments by sequence number for each segment. Connection Control: Connectionless or connection oriented, In connection oriented it makes connection and terminates connections when data transfer completes Flow control: End to end rather than single link Error control: Performed between process to process rather than a single link 01 820 Unit-I introduction 22
Transport layer 01 820 Unit-I introduction 23
Session layer has the following responsibilities • Control for data exchange • Data synchronization • Failure recovery • Communication setup and teardown Enables two applications to have an ongoing conversation or dialog Ability to interrupt and recover as session SQL, RPC, X-Windows 01 820 Unit-I introduction 24
Session layer • The session layer allows users on different machines to establish sessions between them. • Sessions offer various services, including dialog control (keeping track of whose turn it is to transmit), token management (preventing two parties from attempting the same critical operation at the same time), and synchronization (check pointing long transmissions to allow them to continue from where they were after a crash). 01 820 Unit-I introduction 25
Presentation layer Presentation has the following responsibilities Translation: Data is of text, audio or video: changed to bit stream. Different computers use different encoding system. • BMP, WAV, JPEG, MIDI, HTML, ASCII Data encryption: To ensure privacy (Encryption, Decryption) Data compression: To reduce the size of the file 01 820 Unit-I introduction 26
Presentation layer • Presentation layers concerned with the syntax and semantics of the information transmitted. • In order to make it possible for computers with different data representations to communicate, the data structures to be exchanged can be defined in an abstract way, along with a standard encoding to be used ''on the wire. '' • The presentation layer manages these abstract data structures and allows higher-level data structures (e. g. , banking records), to be defined and exchanged. 01 820 Unit-I introduction 27
Application layer The port numbers are divided into three ranges: the well-known ports, the registered ports, and the dynamic or private ports. The well-known ports are those from 0 through 1023. Examples include: 20 & 21: File Transfer Protocol (FTP) 22: Secure Shell (SSH) 23: Telnet remote login service 25: Simple Mail Transfer Protocol (SMTP) 53: Domain Name System (DNS) service 80: Hypertext Transfer Protocol (HTTP) used in the World Wide Web 3128: Port used by some proxy servers, Web caches and the default for the Squid cache 110: Post Office Protocol (POP 3) 119: Network News Transfer Protocol (NNTP) 143: Internet Message Access Protocol (IMAP) 161: Simple Network Management Protocol (SNMP) 443: HTTP Secure (HTTPS) 465: SMTP Secure (SMTPS) 01 820 Unit-I introduction 28
Application layer • The application layer contains a variety of protocols that are commonly needed by users. • HTTP (Hyper Text Transfer Protocol) • Other application protocols are used for file transfer, electronic mail, and network news. 01 820 Unit-I introduction 29
Application layer Application has the following responsibilities • Initiate request for network services • Provides network services to applications such as email and Web browsers Protocols and utilities • Telnet • FTP • DNS • SMTP • SNMP 01 820 Unit-I introduction 30
Associated TCP/IP Protocols & Services HTTP Hypertext Transfer Protocol. The core of the World Wide Web, facilitates retrieval and transfer of hypertext (mixed media) documents. Telnet A remote terminal emulation protocol that enables clients to log on to remote hosts on the network. SNMP Simple Network Management Protocol. Used to remotely manage network devices. Stands for the Simple Network Management Protocol. DNS Provides meaningful names like achilles. mycorp. com for computers to replace numerical addresses like 123. 45. 67. 89. Stands for the Domain Name System. SMTP Simple Mail Transfer Protocol which gives simple electronic mail facilities. FTP File Transfer Protocol is the standard way to transfer files between different machines. Needs FTP client program on computer. 01 820 Unit-I introduction 31
Data Encapsulation • It is a process of adding a header to wrap the data that flows down the OSI model. Encapsulation Process • Wrapping up of data into a protocol is also known as encapsulation. • The Application layer, Presentation layer and Session layer create data from user's input. • Encapsulation actually starts at layer 4 of the OSI model where the Transport layer convert the data into segments by adding a header containing source and destination port numbers. • The Network layer convert the segments into packets (or datagram) by adding a header containing source and destination IP address. • The Data link layer convert the packets into Frames by adding a header containing source and destination MAC address and a trailer containing the Frame check sequence(FCS)used for verifying the data integrity. • The Physical layer convert the frames to bits and it is transmitted through the physical medium which can be a UTP 01 820 Unit-I introduction 32
Data Encapsulation 01 820 Unit-I introduction 33
Data Encapsulation 01 820 Unit-I introduction 34
Summary of layers 01 820 Unit-I introduction 35
Some Data Comm. Standards Layer Common Standards 5. Application layer HTTP, HTML (Web) MPEG, H. 323 (audio/video) IMAP, POP (e-mail) 4. Transport layer TCP (Internet) SPX (Novell LANs) 3. Network layer IP (Internet) IPX (Novell LANs) 2. Data link layer Ethernet (LAN) Frame Relay (WAN) PPP (dial-up via modem for MAN) 1. Physical layer RS-232 c cable (LAN) Category 5 twisted pair (LAN) V. 92 (56 kbps modem) 01 820 Unit-I introduction 36
TCP/IP PROTOCOL SUITE • Developed prior to the OSI model. • The layers in the TCP/IP protocol suite do not exactly match those in the OSI model. • The original TCP/IP protocol suite was defined as having four layers: host-to-network, internet, transport, and application. • However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and application. 01 820 Unit-I introduction 37
TCP/IP and OSI model 01 820 Unit-I introduction 38
TCP/IP and OSI Model • Simple Mail Transfer Protocol (SMTP) • File Transfer Protocol (FTP) • Hypertext Transfer Protocol (HTTP) • Domain Name System (DNS) • Simple Network Management Protocol (SNMP) • Stream Control Transmission Protocol (SCTP) • Transmission Control Protocol (TCP) • User Datagram Protocol (UDP) • Internet Control Message Protocol (ICMP) • Internet Group Management Protocol (IGMP) • Internet Protocol (IP) • Address Resolution Protocol (ARP) • Reverse Address Resolution Protocol (RARP) 01 820 Unit-I introduction 39
Physical and Data Link Layers Covers physical interface between PC or workstation and a transmission medium or network At the physical and data link layers, TCP/IP does not define any specific protocol. It supports all the standard and proprietary protocols. A network in a TCP/IP internetwork can be a local-area network or a wide-area network. 01 820 Unit-I introduction 40
Network Layer Concerned with access to and routing data across a network for two end systems attached to the same network. TCP/IP supports the Internetworking Protocol. IP uses four supporting protocols : ARP, RARP, ICMP, and IGMP. v IP (Internetworking Protocol) v ARP (Address Resolution Protocol) v RARP (Reverse Address Resolution Protocol) v ICMP (Internet Control Message Protocol) v IGMP (Internet Group Message Protocol) v. Internet Layer: IP provides the routing functions across the multiple networks 01 820 Unit-I introduction 41
Network Layer IP (Internetworking Protocol) • IP is the transmission mechanism by the TCP/IP protocol. • It is unreliable connectionless protocol a best effort delivery service. • It transports data in packets called datagrams. ARP (Address Resolution Protocol) • Is used to associate a logical address with a physical address. ARP is used to find the physical address of the node when its Internet address is known. RARP (Reverse Address Resolution Protocol) • It allows a host to discover its Internet address when it knows only physical address. It is used when a computer is connected for the first time. 01 820 Unit-I introduction 42
Network Layer ICMP (Internet Control Message Protocol) • ICMP is mechanism used by host and gateways to send notification of datagram problems back to the sender. IGMP (Internet Group Message Protocol) • IGMP is used to facilitate the simultaneous transmission of message to a group of recipients. 01 820 Unit-I introduction 43
Transport Layer Collection of mechanisms in a single and common layer The transport layer was represented in TCP/IP by two protocols : TCP and UDP. IP is a host-to-host protocol TCP and UDP are transport level protocols responsible for delivery of a message from a process to another process. UDP (User Datagram Protocol) TCP (Transmission Control Protocol) SCTP (Stream Control Transmission Protocol) 01 820 Unit-I introduction 44
Transport Layer UDP (User Datagram Protocol) • UDP is the simper of the two standard TCP/IP transport protocol. It is a process to process protocol that adds only port address, checksum, error control. TCP (Transmission Control Protocol) IP is a host-to-host protocol • TCP is a reliable stream transport protocol (connection oriented) • At the sending end message is divided into smaller units called segments. SCTP (Stream Control Transmission Protocol) • Supports for newer applications such as voice over IP. It combiners the best features of UDP and TCP. 01 820 Unit-I introduction 45
What is TCP/IP? Transmission Control Protocol (TCP) – uses a set of rules to exchange messages with other Internet points at the information packet level Internet Protocol (IP) – uses a set of rules to send and receive messages at the Internet address level TCP/IP is a result of protocol research and development conducted on experimental packet switched network by ARPANET funded by the defense advanced research projects agency (DARPA). TCP/IP used as internet standards by the internet architecture board (IAB). 01 820 Unit-I introduction 46
IP Connectionless protocol (I. e. no established connection between the end points that are communicating. ) Responsible for delivery the independently treated packet !!!! TCP responsible for reassembly. 01 820 Unit-I introduction 47
Application Layer The application layer in TCP/IP is equivalent to the combined session, presentation, and application layers in the OSI model. Many protocols are defined at this layer. Contains the logic needed to support the various user applications. Separate module are required for each application 01 820 Unit-I introduction 48
Associated TCP/IP Protocols & Services HTTP Hypertext Transfer Protocol. The core of the World Wide Web, facilitates retrieval and transfer of hypertext (mixed media) documents. Telnet A remote terminal emulation protocol that enables clients to log on to remote hosts on the network. SNMP Simple Network Management Protocol. Used to remotely manage network devices. Stands for the Simple Network Management Protocol. DNS Provides meaningful names like achilles. mycorp. com for computers to replace numerical addresses like 123. 45. 67. 89. Stands for the Domain Name System. SMTP Simple Mail Transfer Protocol which gives simple electronic mail facilities. FTP File Transfer Protocol is the standard way to transfer files between different machines. Needs FTP client program on computer. 01 820 Unit-I introduction 49
RS-232 01 820 Unit-I introduction 50
RS-232 D-Type-9 pin no. Pin outs Function 3 2 RD Receive Data (Serial data input) 2 3 TD Transmit Data (Serial data output) 7 4 RTS 8 5 CTS 6 6 DSR Request to send (acknowledge to modem that UART is ready to exchange data Clear to send (i. e. ; modem is ready to exchange data) Data ready state (UART establishes a link) 5 7 SG Signal ground 1 8 DCD 4 20 DTR Data Carrier detect (This line is active when modem detects a carrier Data Terminal Ready. 9 01 820 D-Type 25 pin no. 22 RI Ring Indicator (Becomes active when modem detects ringing signal from PSTN Unit-I introduction 51
Max 232 01 820 Unit-I introduction 52
Parallel Port 01 820 Unit-I introduction 53
ADDRESSING Four levels of addresses are used in an internet employing the TCP/IP protocols: physical, logical, port, and specific. 01 820 Unit-I introduction 54
Relationship of layers and addresses in TCP/IP 01 820 Unit-I introduction 55
Physical Addressing • A network adapter has a unique and permanent physical address. • A Physical address is also called MAC address is a 48 bit flat address burned into the ROM of the NIC (Network Interface Card) card at the factory which is a Layer 1 device of the OSI model. • On a local area network, low-lying hardware-conscious protocols deliver data across the physical network using the adapter's physical address. • On a basic ethernet network, for example, a computer sends messages directly onto the transmission medium. • The network adapter of each computer listens to every transmission on the local network to determine whether a message is addressed to its own physical address. 01 820 Unit-I introduction 56
Physical Addressing (Network Interface Card) 01 820 Unit-I introduction 57
Physical Addressing 01 820 Unit-I introduction 58
Physical addresses A node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link (bus topology LAN). The computer with physical address 10 is the sender, and the computer with physical address 87 is the receiver. 01 820 Unit-I introduction 59
Most local-area networks use a 48 -bit (6 -byte) physical address written as 12 hexadecimal digits; every byte (2 hexadecimal digits) is separated by a colon, as shown below: 07: 01: 02: 01: 2 C: 4 B A 6 -byte (12 hexadecimal digits) physical address. 01 820 Unit-I introduction 60
Logical Addressing • Logical address is necessary for universal communication. • A Logical address also called IP address is a 32 - bit address assigned to each system in a network. • No two publicly addressed and visible host on the Internet can have the same IP address. • This works in Layer-3 of OSI Model. • This would be generally the IP address. 01 820 Unit-I introduction 61
Logical Addressing 01 820 Unit-I introduction 62
Logical Addressing 01 820 Unit-I introduction 63
Logical Addressing 01 820 Unit-I introduction 64
Logical Addressing 01 820 Unit-I introduction 65
IP Addresses Two routers connecting three LANs. Each device (computer or router) has a pair of addresses (logical and physical) for each connection. In this case, each computer is connected to only one link and therefore has only one pair of addresses. Each router, however, is connected to three networks (only two are shown in the figure). So each router has three pairs of addresses, one for each connection. 01 820 Unit-I introduction 66
IP Addresses 01 820 Unit-I introduction 67
The physical addresses will change from hop to hop, but the logical addresses usually remain the same. 01 820 Unit-I introduction 68
Port Address A single wire connects the network to the distant computer, but there may be many applications on that machine-a web server, an ftp server, a telnet server, etc. -waiting for somebody to connect. So the question arises: How do you use one wire and one IP address to connect to the right application? The answer: Ports. Port address is transport layer ID (simillar to IP in Network Layer) which identify the application on the host. The address for a device as it is identified at the Media Access Control (MAC) layer in the network architecture. MAC address is usually stored in ROM on the network adapter card and is unique. Telnet Port 23 Mail (smtp, or send mail) Port 25 World Wide Web Post Office (pop, or get mail) Port 110 News (nntp) 01 820 Port 80 Port 119 Unit-I introduction 69
A port address is a 16 -bit address represented by one decimal number as shown. 753 A 16 -bit port address represented as one single number. 01 820 Unit-I introduction 70
Port Address The sending computer is running three processes at this time with port addresses a, b, and c. The receiving computer is running two processes at this time with port addresses j and k. Process a in the sending computer needs to communicate with process j in the receiving computer. Note that although physical addresses change from hop to hop, logical and port addresses remain the same from the source to destination. 01 820 Unit-I introduction 71
Port addresses 01 820 Unit-I introduction 72
Port addresses 01 820 Unit-I introduction 73
Application layer The port numbers are divided into three ranges: the well-known ports, the registered ports, and the dynamic or private ports. The well-known ports are those from 0 through 1023. Examples include: 20 & 21: File Transfer Protocol (FTP) 22: Secure Shell (SSH) 23: Telnet remote login service 25: Simple Mail Transfer Protocol (SMTP) 53: Domain Name System (DNS) service 80: Hypertext Transfer Protocol (HTTP) used in the World Wide Web 110: Post Office Protocol (POP 3) 119: Network News Transfer Protocol (NNTP) 143: Internet Message Access Protocol (IMAP) 161: Simple Network Management Protocol (SNMP) 443: HTTP Secure (HTTPS) 465: SMTP Secure (SMTPS) 01 820 Unit-I introduction 74
Application layer Specific Address Email address, manjup. jnnce@gmail. com and the Universal Resource Locater (URL) ex: www. google. co. in 01 820 Unit-I introduction 75
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